**Question:** All of the following statements are true regarding Staphylococci except -

A. Staphylococci are Gram-positive cocci in clusters
B. Staphylococci produce an enzyme that causes yellow pigmentation in blood agar plates
C. Staphylococci cause only mild skin infections
D. Staphylococci are always susceptible to penicillin

**Correct Answer:** C. Staphylococci cause only mild skin infections

**Core Concept:** Staphylococci are a group of bacteria that are Gram-positive cocci in clusters. They can cause various infections in humans and animals, ranging from mild skin infections to life-threatening diseases.

**Why the Correct Answer is Right:** Staphylococci are classified as Gram-positive cocci in clusters because they exhibit a specific arrangement of their cell wall structure. They can cause mild skin infections due to their ability to invade the skin and soft tissue, leading to symptoms like impetigo, boils, and furuncles.

**Why Each Wrong Option is Incorrect:**

A. Staphylococci are indeed Gram-positive cocci in clusters, making this statement incorrect.
B. While some Staphylococci species produce enzymes responsible for yellow pigmentation in blood agar plates, this statement is not universally true for all Staphylococci species.
D. Although penicillin is a common antibiotic used to treat Staphylococcal infections, not all Staphylococci are susceptible to penicillin. Some strains can develop resistance through various mechanisms, such as beta-lactamase production.

**Clinical Pearl:** Understanding the pathophysiology and antibiotic susceptibility patterns of Staphylococci is crucial for accurate diagnosis and treatment of infections caused by these bacteria. Knowing the clinical spectrum of diseases caused by Staphylococcus species helps medical professionals select the most appropriate antibiotics and treatment strategies for a patient's condition.

✓ Correct Answer: C. Expression of methicillin resistance in Staphylococcus aureus increases when it is incubated at 37°C on blood agar.